Genetic information, variation and relationships between organisms Flashcards
Describe the appearance of DNA molecules in prokaryotic cells
Short, circular, unassociated with proteins
Describe the appearance of DNA molecules in eukaryotic cells
Very long, linear, associated with proteins called histones
What are histones?
The proteins associated with DNA molecules in eukaryotic cells
What is a gene?
A base sequence of DNA that codes for:
the amino acid sequence of a polypeptide
a functional RNA
What is a locus?
A term used to refer to the fixed position a gene occupies on a particular DNA molecule
Which 3 key terms describe the genetic code?
Universal, non-overlapping, degenerate
Why is the genetic code ‘degenerate’?
Most amino acids are coded for by more than one triplet
What is a triplet codon? (in terms of DNA)
A sequence of three DNA nucleotide bases which code for a specific amino acid
Only introns code for amino acid sequences. True or false?
FALSE. Only EXONS code for amino acid sequences
Genetic code is referred to as ‘non-overlapping’. What does this mean?
Each base in the sequence is read only once
Genetic code is generally ‘universal’. What does this mean?
Bar a few minor exceptions each triplet codes for the same amino acid in all organisms.
Which feature of genetic code is indirect evidence of evolution?
The universal nature of genetic code
What are stop codons?
Three bases (one codon) that do not code for any amino acids
During splicing, what part of the pre-mRNA is got rid of?
Introns
What is a homologous pair of chromosomes?
A pair of chromosomes containing one maternal and one paternal chromatid joined at the centromere. They carry the same genes but may have different alleles
What is an allele?
A different version of the same gene
What is the genome?
The complete set of genes in a cell (including those in the mitochondria and/or chloroplast
What is the proteome?
The full range of proteins produced by the genome
How does the complete proteome differ from the proteome?
The complete proteome is the full range of proteins produced by a given cell type under certain conditions
Give three differences between DNA and mRNA
DNA is double stranded, mRNA is single
DNA has a double helix, mRNA has a single
DNA has deoxyribose pentose sugar, mRNA has ribose
DNA has AGCT, mRNA has AGCU
DNA is v stable, mRNA is less stable than DNA
DNA’s quantity is constant for all cells of a species (bar gametes), mRNA’s quantity varies from cell to cell w/ level of metabolic activity
‘Double stranded’ describes the structure of DNA, mRNA or tRNA?
DNA
‘Single stranded’ describes the structure of DNA, mRNA or tRNA?
mRNA and tRNA
Which is the largest structure of tRNA, mRNA and DNA?
DNA
Which is the smallest structure of DNA, tRNA and mRNA?
tRNA
Which structure, of DNA, tRNA and mRNA has a double helix?
DNA
Which structure, of DNA, tRNA and mRNA has a single helix?
mRNA
Which structure, of DNA, tRNA and mRNA has a clover shape?
tRNA
Which structure, of DNA, tRNA and mRNA has a deoxyribose pentose sugar?
DNA
Which structure, of DNA, tRNA and mRNA has a ribose pentose sugar?
mRNA and tRNA
Which structure, of DNA, tRNA and mRNA has the bases: adenine, uracil, guanine and cytosine?
mRNA and tRNA
Which structure, of DNA, tRNA and mRNA has the bases: adenine, thymine, guanine and cytosine?
DNA
Which structure, of DNA, tRNA and mRNA is mostly found in the nucleus?
DNA
Which structure, of DNA, tRNA and mRNA is made in the nucleus but can be found throughout the cell?
mRNA and tRNA
Which structure, of DNA, tRNA and mRNA is the most stable?
DNA
Which structure, of DNA, tRNA and mRNA is the least stable?
mRNA
What is transcription?
The process of making pre-mRNA using part of the DNA as a template
Describe how pre-mRNA is formed from DNA
Transcription
DNA helicase breaks H bonds b/w bases to allow the strands to unwind and expose the bases
Free nucleotide bases pair w/ their complementary bases on one of the strands (template strand)
RNA polymerase attracted to promoter region on the strand –> goes along joining the nucleotides (phosphodiester bonds) together to form pre-mRNA
As RNA polymerase moves along, DNA rejoins behind it
RNA polymerase detaches until it reaches a stop codon
What is the role of RNA polymerase in transcription?
To join free nucleotides to those on the template strand
Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell (6) PPQ
- Helicase;
- Breaks hydrogen bonds;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- (Attraction) according to base pairing rule;
- RNA polymerase joins (RNA) nucleotides together;
- Pre-mRNA spliced to remove introns
What is splicing?
The process by which introns are removed from pre-mRNA to form mRNA
What is translation?
The process by which mRNA is used to make an amino acid chain, and so a protein
Describe what happens during translation
A ribosome attaches to the starting codon atone end of the mRNA molecule
tRNA molecule w/ the complementary anticodon moves the the ribosome and pairs w/ the codon on mRNA
Another tRNA w/ the complementary anticodon for the next codon pairs
The 2 amino acids on the tRNA are joined by a peptide bond using an enzyme and ATP
Ribosome moves one codon along the mRNA - 1st tRNA released, another joins
Process repeats, building up a chain until the ribosome reaches a stop codon
What is a gene mutation?
Any change to one or more nucleotide bases, or a change in base sequence
What is a base substitution mutation?
When a nucleotide is replaced by another nucleotide with a different base
What is a deletion mutation?
When a nucleotide is lost from the normal DNA sequence
Results in a frame shift - all bases shifted forward resulting in different sets of triplets and so different code
How many chromosomes does a human somatic cell contain?
46 (23 pairs)
What are the stages of meiosis?
Meiosis I and meiosis II, each containing prophase, metaphase, anaphase and telophase
What happens during prophase I?
Chromosomes shorten/thicken to become visible
Nuclear envelope disintegrates
Homologous pairs associate w/ each other (line up next to each other)
Crossing over occurs
What does crossing over involve?
The exchange of of alleles b/w chromatids/chromosomes
What happens during metaphase I?
Chromosomes line up at the equator
–> independent assortment (random position in the line)
Spindle fibres attach to the centromere
What happens during anaphase I?
Chromosomes are pulled apart to opposite poles by the spindle fibres
What happens during telophase I?
Spindle fibres disintegrate
Cytokinesis begins - cell splits in 2
What happens during prophase II?
Spindle fibres start to form at poles
What happens during metaphase II?
Chromosomes line up at the equator
Spindle fibres attach to the centromere
What happens during anaphase II?
Sister chromatids pulled away by spindle fibres
What happens during telophase II?
Cytokinesis - cell splits (now have 4 genetically different)
Nuclear envelope reforms
How does genetic variation occur in meiosis?
Independent segregation/assortment
Crossing over
Random fertilisation
What is genetic diversity?
The total no. of different alleys in a population
Also a factor in allowing natural selection to occur
Describe and explain how natural selection leads to evolution
W/in any population there will be a gene pool containing a wide variety of alleles
Random mutation –> possibly results in new allele
Most cases = harmful but sometimes advantageous
w/ allele = better adapted and so more likely to survive
Therefore more likely to successfully breed (more likely to get resources, grow more rapidly) and so produce offspring
Only those who successfully reproduce will pass on their alleles to the next gen. therefore advantageous allele more likely to be passed on
These offspring are also more likely to survive and reproduce successfully
Over time, frequency of advantageous increases, non-advantageous decreases
What is directional selection?
Where one extreme is favoured over others, causing the allele frequency to shift in the direction of that phenotype
What is stabilising selection?
Where individuals w/ phenotypes closest to the mean are favoured (if environmental conditions remain stable)
Phenotypes at the extremes are less likely to pass on their alleles, therefore extremes tend to be eliminated
Define what is meant by the term ‘species’
A group of anatomically, biochemically and genetically similar organisms that are capable of interbreeding to produce gentle offspring
What are the two ways of classifying a species?
Artificial classification
Phylogenetic classification
How does artificial classification work?
Groups based on their analogous/comparable characteristics e.g. wings
What are two problems with artificial classification?
No genetic relation
More differences than similarities
Doesn’t show how they’re related
How does phylogenetic classification work?
Base upon evolutionary r/ships b/w organisms and their ancestors
Groups using shared features derived from ancestors
Arranges groups into hierarchy
State the phylogenetic hierarchy from largest to smallest
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
Using the binomial system of naming, what does the 1st name represent?
The genus of the organism
Using the binomial system of naming, what does the 2nd name represent?
The species of the organism
Why is courtship behaviour important?
To ensure mating is successful and offspring have the max. chance of survival
Describe how courtship behaviour can help ensure successful mating
Enables individuals to: Recognise members of their own species Identify a mate that is capable of breeding Form a pair bond Synchronise mating Become able to breed
Explain how being able to recognise members of their own species increases the chance of successful mating and so offspring survival
Only members of the same species produce fertile offspring
Explain how being able to synchronise mating increases the chance of successful mating and so offspring survival
Time at which there’s the max. probability of sperm and egg meeting
Define ‘biodiversity’
A general term used to describe variety in the living world
What is species diversity?
A term to refer to the no. of different species and the no. of individuals of each species w/in any on community
What is genetic diversity?
A term to refer to the genes possessed by the individuals that make up a population of a species
What is ecosystem diversity?
A term used to refer to the range of different habitats, from a small local habitat, to the whole earth
What is species richness?
The no. of different species in a particular area at a given time
What is index of diversity a measure of?
Species richness
How do you calculate index of diversity?
d = N(N-1) / Total n(n-1)
where:
d = index of diversity
N = total no. of organisms of all species
n = total no. of organisms of each species
Describe and explain how agricultural ecosystems affect species diversity
Specific species grown to increase productivity, thus reducing allele variation
Increase no. of specific species to make it economical –> area has room for only so much biomass, and if the majority of this is the specific species, that doesn’t leave much room for others –> therefore increases competition
Pesticide use actively excludes unwanted species
Overall species richness decreases
Give 5 examples of farming techniques that reduce species diversity
Removal of hedgerows Creation of monocultures Filling in of ponds Drainage of marshes and other wetlands Overgrazing of land Use of pesticides and inorganic fertilisers Escape of effluent (sewage/liquid waste) into water courses Absence of crop rotation
Give 5 examples of conservation techniques
Maintain existing hedgerows at the most beneficial height/length
Plant hedges as field boundaries rather than using fences
Maintain existing ponds and create new where possible
Plant native trees on land w/ a low species diversity
Reduce use of pesticides –> bio control where possible or GM crops
Use of organic fertilisers
Use of crop rotation that includes a nitrogen fixing crop
Name 4 ways someone could investigate diversity
Look at: observable characteristics DNA base sequences mRNA base sequences protein amino acid sequences
Give two limitations of using observable characteristics to investigate diversity
Large no. of characteristics coded for by more than one gene
Vary continuously
Characteristics can also be modified by the environment
